This invention relates to a centrifugal machine in which centrifugal force is applied to a sample for effecting separation or precipitation, more particularly, a so-called swinging type rotor wherein buckets containing the sample are hung on arms of the rotor and rotated thereby.
One example or a so-called Beckman type centrifugal machine is disclosed in U.S. Pat. No. 4,009,824 issued to Herchel E. Wright on Mar. 1, 1977. The centrifugal machine disclosed therein comprises a plurality of radially extending arms which are equally spaced apart in the circumferential direction. Each arm is provided with a single opening near the outer end thereof perpendicularly to the longitudinal axis of the arm. A trunnion pin is inserted through the opening and has arcuately oriented opposite extremities acting as trunnions. Buckets are swingably hung on opposing extremities of adjacent arms. With this construction, the diameter of the openings through which the trunnion pins extend to become large, thus increasing the thickness of the arms. To obviate this difficulty, it is necessary to make the trunnion pins thin. When the diameter of the trunnion pins is reduced it is necessary to make them with a material having a high mechanical strength. This, however, reduces the bearing areas of the buckets so that it is necessary to make also the bucket with a strong materials. These limitations increases the cost of manufacturing.
Another prior art swinging type rotor is shown in FIGS. 1 and 2 of the accompanying drawings. A rotor 11 shown therein has an opening 13 at the central portion thereof 12 to receive a rotating shaft of a driving motor not shown. A plurality of integral arms 14 equally spaced apart in the circumferential direction extend in the radial direction. At the outer end of each arm are inserted trunnion pins 15, the axes thereof intersecting at an angle. Buckets 16 are hung on opposing trunnion pins 15 adjacent arms 14. More particularly, each bucket is guided by a pair of parallel recesses 17 formed on both sides of the bucket so that the upper ends of the recesses 17 engage the ends of the trunnion pins to hang the buckets to be swingable about the axes of the opposing trunnion pins. Although in FIGS. 1 and 2 only one bucket is shown it will be clear that six buckets are hung in the construction shown. As the rotor 11 is rotated, the buckets are swung from the dotted line position to the solid line position as shown in FIG. 2.
In the swinging type rotor, because the spacings between adjacent arms are narrow, it has been impossible or difficult to form openings for receiving the trunnion pins by insterting a tool into the narrow gaps between adjacent arms. For this reason, according to a prior art method of machining, openings 18 for receiving the trunnion pins 15 were formed through opposite side surfaces of the outer end of each arm. The axes of the openings 18 make acute angles with respect to the center line of each arm and the axes of the trunnion pins received in a pair of openings 18 of each arm cross each other with an angle. Accordingly, the thickness of the portions 19 on the outsides of the openings 18 as viewed from the center of the rotor 11 is small, so that these thin portions 19 would be ruptured or deformed under a strong centrifugal force. Rupture of the portions 19 results in fly off of the buckets thus causing a serious damage especially when the rotor is rotated at an extremely high speed.